This is a master bug to track the implementation of HTML5 Microdata for WebKit.
Microdata is a specification used to nest semantics within existing content on web pages. Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience for users. Microdata helps technologies such as search engines and web crawlers better understand what information is contained in a web page, providing better search results.
Here is the spec : http://www.whatwg.org/specs/web-apps/current-work/multipage/links.html#microdata